1. Field of the Invention
The present invention relates to the field of pedal cycles. More particularly, the invention relates to an electrically assisted cycle kit for fitting to a pedal cycle, a pedal cycle fitted with the kit, a method of fitting the kit to the pedal cycle, and an attachment for attaching an object to a pedal cycle.
2. Introduction
Electrically assisted pedal cycles include an electric motor for assisting with pedal cycle motion of the cyclist. The drive of the motor is typically controlled based on the pedalling speed of the cyclist, so that the motor provides assistance when the cyclist is pedalling but does not drive when the cyclist brakes or stops pedalling. To enable safe regulation of the drive of the motor, the cycle is typically provided with sensors for sensing the speed at which the cyclist is pedalling. Various kinds of sensors may be used to sense the pedalling speed, including simple proximity switches which sense a magnet fixed to a rotating target (e.g. a wheel) on each rotation of the target; Hall sensors which sense a number of magnetic targets arranged on a specially made target disc fitted to the wheel of the cycle; and light sensors where a disk with holes is used so that light can be detected through each target hole.
The key disadvantage of such sensors is that they require a manufactured target device to be made in each case and fixed accurately and robustly to the pedal cycle for it to work. Given the very wide range of pedal cycle configurations possible, satisfying every eventuality is very difficult and fitting is not easy. While proximity sensors using a single magnetic target may be easier to fit than the other kinds of sensors and targets, the proximity sensors cannot determine the direction of rotation, which is important for electrically assisted pedal cycles. Other sensors have limits on the number of targets that can realistically be placed on a disc and fitted to any pedal cycle. The resulting limited number of targets limits sensitivity and this can create difficulties in complying with international standards for electric bicycles. Consequently many quality electric bicycle manufacturers use torque sensors which are very difficult to retro-fit to pedal cycles and often result in highly variable power assistance.
Therefore, the present invention seeks to provide an electrically assisted cycle kit which provides high quality sensing of the pedalling of the cyclist, while being easy to fit to a pedal cycle, even if fitted by someone who is not an expert.